I think there parent comment just meant that implementation dependent is technically not the same as hardware dependent. For example, the size of int is not sp

I think there parent comment just meant that implementation dependent is technically not the same as hardware dependent. For example, the size of int is not specified by the standard, as you said. But it can still be different from the natural word size of the underlying hardware, if the compiler vendor chooses to make it so. Case in point is int on 64-bit platforms is usually 32-bit in practice. In Microsoft's compiler, even long int is 32-bit even on 64-bit hardware.